The historical maps, letters and manuscripts in Australia's biggest library are soon to be joined by another form of social document - pornographic Web sites.

The National Library of Australia says building up a collection of sex Web sites is just as important as maintaining the rest of its archive of five million books and magazines, 40,000 drawings and paintings, and more than half a million photographs.

The library in the capital, Canberra, already holds an extensive collection of pornographic magazines, including copies of Bra Busters and Big 'n' Bouncy.

Writing in the library's latest newsletter, electronics librarian Edgar Crook said the collection would help build up 'a representative picture of Australian erotica on the Internet'.

'The examination of society and culture of a period by necessity involves the study of its sexual life. The erotic matter created in, for example, the Victorian era is of great interest to the modern historian,' he said. 'The surviving sexual diaries and pornographic novels of this era provide insight into ordinary lives that are just as important as those provided by the many 'improving' works or the social novels that are still so widely enjoyed.'

The adult sites will be added to the library's growing online collection. It also has a collection of gay erotica dating back to the 1970s.

Mr Crook said that while the initiative might prompt sniggers, it was an important part of the library's remit to 'preserve a comprehensive collection of documentary materials relating to Australia and Australians'.

The researchers have been told not to exclude material some people might regard as controversial or offensive. Mr Crook said adult sex sites were 'an indicator of social mores, standards and public attitudes to matters sexual'.

'With this in mind, it is clear that there is no merit in being coy today and therefore delivering an incomplete picture to future researchers.'

He said the pornography would not be available for 'the salacious enjoyment of the contemporary reader'.